Although footwear science has made considerable progress in the last decade, a performance gap continues to exist between standard issue military footwear and expedition footwear available on the commercial market. While the provision of in-shoe foot orthoses (ISFOs) is commonplace in commercial athletic and outdoor footwear, the provision of similar devices that can be accommodated in military footwear has not received significant attention. The high rates of lower extremity injuries in the military point to the urgent need to close the footwear performance gap by providing military personnel with footwear and in-boot orthoses that incorporate up-to-date biomechanical knowledge and state-of-the-art materials.